558 Introduction to the Study of Science 



4. What measures are taken to get rid of dust? 5. What are the 

 advantages and disadvantages of oiled floors? 6. How does water 

 vary in usefulness ? 7. How can hard water be softened ? 8. Of what 

 materials is street dust made up? 9. How may disease germs be 

 carried by dust? 



10. What is a "culture"? 11. Describe the preparation of cul- 

 tures. 12. What is the object of boiling the potatoes used for 

 cultures and sterilizing the containers? 13. What conditions are 

 necessary for the growth of molds? 14. What is meant by a con- 

 trol culture? 15. What colors may molds have? What does the- 

 color indicate? 



16. Describe how molds reproduce. 17. Will molds start to grow 

 where no spores are planted? 18. To what group of plants do molds 

 belong? 19. To what other plants are they related? 



20. Compare fungi and green plants as to the source of their food 

 materials; the character of their work. 21. What are saprophytes? 

 22. How are saprophytic molds useful in nature? 23. How are they 

 useful in industries? 24. Explain the changes in cheese effected by 

 molds. 25. What undesirable effects do molds produce in foods? 

 26. How are parasitic molds distinguished from saprophytes ? 27. What 

 is a host ? 28. What is the relation of certain fungi to human health ? 

 To the health of the housefly? To the health of plants? 29. Account 

 for the universal distribution of molds. 30. What natural conditions 

 are molds fitted to survive? 31. Of what use is the knowledge of their 

 rate of growth? 32. Summarize the conditions favoring the growth 

 of molds. 33. How may knowledge of these conditions be used in 

 preventing their growth or destroying the spores? 



III. YEASTS 



279. Other plants distributed in the air. Molds comprise 

 only a small part of the known list of invisible plants that are 

 present in and distributed by the atmosphere. The conditions 

 that are especially favorable to molds, like those secured in 

 your experiments, are not equally favorable to all kinds of in-- 

 visible plants or their spores, or at least do not make their 

 products visible. Consequently we must provide different 

 and suitable conditions just as a gardener provides different 

 kinds of soil for various plants in the garden. One of the 

 simplest ways of cultivating certain other kinds of air-dis- 



